The present invention relates to a copper foil with a carrier that is used in producing a single-sided or multilayer laminated plate of two or more layers for use in a print wiring board.
A typical example of a multilayer laminated body is a printed circuit board. Generally, a printed circuit board is basically configured from a dielectric material referred to as a “prepreg” that is obtained by impregnating synthetic resin in a base material such as a synthetic resin plate, glass plate, nonwoven glass fabric or paper.
A sheet such as a copper or copper alloy foil having electrical conductivity is bonded to the prepreg surface, and to both of the front and back surfaces. A laminate that is assembled as described above is generally referred to as a CCL, namely, a Copper Clad Laminate material. When copper foils are multi-layered on the CCL material with use of the prepreg, this is referred to as a multilayer board.
Other foils made of aluminum, nickel, zinc or the like may also be used in substitute for the copper or copper alloy foil. The foil thickness is roughly 5 to 200 μm.
In the foregoing process, a copper foil with a carrier is used for the purpose of preventing the adhesion of foreign matter on the surface of the copper foil and for the purpose of improving the handling ability.
For example, in the method of producing a four-layer substrate using a conventionally known copper foil with a carrier (refer to Patent Documents 2, 3, 4), an ultrathin copper foil to which a carrier is peelably bonded is mounted on a stainless pressing plate called “mirror plate”) having a flat pressing surface with a thickness of 0.2 to 2 mm so that the M surface is on top (‘M surface’ as used herein represents ‘rough surface’, and both of the expressions are used interchangeably hereinafter), subsequently a prescribed number of prepregs, subsequently a printed circuit board in which a circuit is formed on a CCL material referred to as the inner layer core, subsequently a prepreg, and subsequently an ultrathin copper foil to which a carrier is peelably bonded are mounted so that the M surface is at the bottom, and by laminating these in the order of the mirror plate, an assembled unit configured from one set of a four-layer substrate material is thereby complete.
Subsequently, these units called “pages” are repeatedly laminated 2 to 10 times to configure a press assembly called “book”. Subsequently, the foregoing book is placed on a hot plate in the hot press and subject to compression molding at a prescribed temperature and pressure to produce a laminated plate. Substrates with four or more layers can be produced by a similar process by increasing the number of layers of the inner layer core.
Here, with the copper foil with a carrier to be used, since the ultrathin copper foil and the carrier are bonded across the entire surface, there is a problem in that considerable force is required for the worker to peel the carrier after lamination, and this is troublesome for the worker.
In addition, as described above, upon performing the lay-up operation, lamination assembly operation, in other words, the worker needs to alternatively repeat the process of lamination so that the M surface of the copper foil is on top or the M surface is at the bottom, and there is a problem in that the work efficiency will deteriorate. Moreover, since the copper foil and the carrier are of the same size, it is difficult to peel one copper foil at a time during the lay-up, which is also a problem in that the workability deteriorates on this point.
Furthermore, as described in Patent Document 1, upon producing a circuit board using CAC having a structure in which a copper foil is bonded to the front and back surfaces of an aluminum plate, an aluminum plate (JIS#5182) is used as a part of the CAC material. However, since the linear expansion coefficient of the aluminum plate is 23.8×10−6/° C. and higher compared to the copper foil (16.5×10−6/° C.) as the constituent material of the substrate and the polymerized prepreg (C stage: 12 to 18×10−6/° C.), a phenomenon (scaling change) where the board size before and after pressing is different than the designed size will occur. This will lead to the misalignment of the circuit in the in-plane direction, and there is a problem in that this will become a cause for deteriorating the production yield.
The linear expansion coefficient at normal temperature of the various materials used in the print wiring board is as follows. It is evident that the linear expansion coefficient of the aluminum plate is fairly higher than the other materials.                Copper foil: 16.5 (×10−6/° C.)        SUS304: 17.3×10−6/° C.        SUS301: 15.2×10−6/° C.        SUS630: 11.6×10−6/° C.        Prepreg (C stage): 12 to 18×10−6/° C.        Aluminum plate (JIS#5182): 23.8×10−6/° C.        
Not directly related to the present invention, there are the following documents as examples related to an ultrathin copper foil with a carrier (Patent Document 2, Patent Document 3, and Patent Document 4).
[Patent Document 1] Japanese Patent No. 3100983
[Patent Document 2] Japanese Published Unexamined Application No. 2005-161840
[Patent Document 3] Japanese Published Unexamined Application No. 2007-186797
[Patent Document 4] Japanese Published Unexamined Application No. 2001-140090